Electrical measuring instrument.



No. 683,622. v Patented 0st. l, 190|. H. 0. HUGH.

ELECTRICAL MEASURING INSTRUMENT.

(Application :Bled July 24, 1901;)

UNTTED STATES PATENT OFFICE.

'IIARRYY O. RUGH, OBV-SANDWICH, ILLINOIS..

ELECTRICAL MEASURING INSTRUIVI ENT-l SPECIFIGATION forming part ofLetters Patent No...683,622, dated October 1, 190.1.

'Application filed July 24, 1901. Serial No. 695521. (No model.)

Tb aZZ whom, t may concern,.-

Be it known that I, HARRYVO. RUGH, a cit-i- Zen of the United States,residing at Sandwich, in the county of Dekalb and State of Illinois,have invented a certain new and useful Improvement in ElectricalMeasuring Instruments, (Case No.1,) of which the following is a full,clear, concise, and exact description, reference being had to theaccompanying drawings, forming a part of this specification. Y

My invention relates to electrical measuring instruments, and moreparticularly to that class of instruments employed in determining theresistance of electrical conductors.

My invention is an improvement upon Wheatstone or electric bridges, andhas for its object the reduction in the number of instrumentalities thathave usually been employed in operating apparatus of this class. The"Wheatstone bridge, as is well understood, comprises a battery whoseterminals are connected to main binding-posts, there being also twosupplemental binding-posts each united with the main binding-post andthemselves directly connected by a conductor, including the testinginstrument. Each of the four conductors uniting the supplementalbinding-posts with the main bindingposts contains resistance, oneconductor being that whose resistance is to be determined, the otherresistances being known. One of these resistances possesses an absoluteor iixed value, while the relative values of the remaining knownresistances are adjustably determined. There are thus provided twoinstruments possessing fixed resistances, one of the instruments beingincluded in one of the conductors uniting a main and supplementalbinding-post, while the other instrument is provided in the conductorthat directly unites the supplemental binding-posts.

It is the object of my invention to dispense with one of theseinstruments, and for that purpose the instrument or resistance includedin the conductor uniting a main and supplemental binding-post isconstructed to act in anadded capacity-that of an indicatorwhile theindicator that is included in the conductor directly uniting thesupplemental binding-posts may be totally eliminated from the circuit.

In combination witlithis apparatus I preferably employ an instrumentserving lto determine the relative lengths of the two sides of theWheatstone bridge that neither contain the testing instrument nor thedevice of unknown resistance, these conductors for the purpose beingpreferably in the form of German-silver wire possessing high resistance.The diagonal conductor, which in the former type of bridges permanentlyunited the supplemental binding-posts, is preferably connected with butone of these binding-posts and is provided at its other terminal with ablade contact for ready'engagementwith any portion of the German-silverconductor.

p I will explain my invention more fully by reference to theaccompanying drawings, in which- Figure 1 is a plan view of aninstrument constructed in accordance with the invention, certain circuitconnections being indicated in dotted lines. Fig. 2 is a simpliiieddiagrammatic view to illustrate more clearly the principle of operationof the instrument.

Like parts are indicated by similar characters of reference throughoutboth views.

The instrument is provided with two main binding-posts or terminals a band two supplemental binding-posts or terminals c d. The mainbinding-posts a b are directly united by a conductor e, including asource of current in the form of a battery f. The bindingposts a and care united by a conductor g, including a testing instrument, preferablyin the form of a head-telephone h, while the binding-posts b and c areadapted for connection with the terminals of the conductor whoseresistance is to be determined, a device a; of unknown resistance beingindicated in this connection. The binding-posts a and d and b and d areunited, respectively, by conductors i and k, formed, preferably, ofGerman silver of, say, twenty-tive ohms resistance in the aggregate,equally divided between the two conductors. These conductors fr' and 7cthus constitute two sides of the bridge1 opposed to the conductors g andthe remaining sides of the bridge, these four conductors thusconstituting a circuit in the form of a IOO quadrilateral. The diagonalZ of this quadrilateral is preferably adjustable, being adapted forconnection with any portion of the conductor t' or the conductor 7o. Thediagonal Z is flXedly attached to the binding-post c and is provided atits other end with a contact-blade m, constituting a stylus, which maybe readily engaged with any portion of the conductor t' or Zr, wherebythe resistance between the main binding-post (L and the blade m and thesaid blade and binding-post b may be relatively determined. 'Ihediagonal Z is preferably free of any indicating device, and itsresistance is preferably very low, though I do not wish to be limited tothis feature. Each of the sides of the quadrilateral thus containsresistance, two of the sides i and 7c having their resistance relativelyadjustable, the third side g having its resistance fixed, while thefourth side, between the posts b and c, contains the conductor whoseresistance is to be determined. The resistance h in addition to itspassive function is also active in determining the unknown resistance ofthe conductor under test. The most effective form of test instrument isa telephonereceiver. In the operation of the apparatus the contact-bladem is shifted over the conductors i and 7c until that point is reached atwhich the receiver-diaphragm is not actuated.

The method of operationmay be described as follows'. If it be supposedthat the blade or shifting contact m is brought into engagement with thebinding-post d., the amount of current through the telephone-receiver orindicator will be decreased upon each application of the said Contact tothe said bindingpost, the resistance of the conductor Z being preferablynegligible, while if said contact or stylus m is touched to the post bthe resistance, including the telephone-receiver and the conductor ofunknown resistance, will be decreased, thereby permitting an increase ofthe current flowing through the telephonereceiver. Between these twoextremes a point is selected by successive applications of the stylus tothe Wire c' Zt where the current through the receiver does not vary uponapplication and removal of the stylus, this point being termed the pointof silence. Thus more or less of the Wire fZ lo is included in shunt ofthe receiver and the conductor under test in determining the resistanceof said conductor. In actual practice the wire t' Zo is subdivided intosections, as indicated in Fig. l, though it is obvious that these twosections may be joined into asingle wire, as diagrammatically indicatedin Fig. 2.

In the construction of the device the instrument is calibrated by theinclusion of resistances of different known values between thebinding-posts Z) and c, and the various points of silence correspondingto the various resistances are marked, as indicated in the drawlings,along the conductors t' and 7c, which for esaeea between the posts b andc, the point of silence corresponding to this resistance may readily bedetermined, which, coinciding with a point of silence located with theprevious known resistance, furnishes to the tester a measurement of theresistance of the conductor under test. In other words, the stylus endis moved along the wire 11 7c to such a point where the shunt about thetelephone comprising the said wire 'L' Zr, the blade m, and theconductor Z is of a resistance that will not cause a variation of thecurrent iiowing through the receiver.- Current constantly tiows throughthe receiver, and when the shunt-circuit established by the contact ofthe blade m with the wire vl 7i; has too much or too little resistancethe current through the receiver will be Varied. A point may be selectedalong the wire Z Z1: for engagement with the blade m which will causethe said shunt to be neither of too much nor too little resistance, butexactly the right resistance to prevent a variation of current in thereceiver. This is the point of silence. It is of course the variation inthe current that causes the operation of the receiver.

yWhile I have herein shown and particularly described the preferredembodiment of my invention, it is obvious that changes may readily bemade without departing from the spirit thereof, and I do not thereforewish to be limited to the precise disclosure herein set forth; but,

Having thus described my invention, I claim as new and Vdesire to secureby Letters Patentl. The combination with a source of current, of threesides of a quadrilateral circuit adapted to receive current from thesaid source, the fourth side of the said quadrilateral being theconductor whose resistance is to be determined, a test-indicatinginstrument included in one of the sides of the quadrilateral, and aconductor Z for inclusion in connection with the remaining two of thethree permanently-provided sides of the quadrilateral and in shunt ofthe test-indicating instrument and the conductor of unknown resistance,substantially as described.

2. The combination with a source of current, of three sides of aquadrilateral circuit adapted to receive current from the said source,the fourth side of the said quadrilateral being the-conductor whoseresistance is to be determined, a test-indicating instrument included inone of the sides of the quadrilateral, and a conductor Z for inclusionin connection with the remaining two of the three permanently-providedsides of the quadrilateral and in shunt of the test-indicatinginstrument and the conductor of unknown resist-` ance, thetest-indicating instrument and the conductor of unknown resistance beingadapted for series connection with each other,while the remaining twosides of the quadrilateral are also in series with each other, the saidsource of current being in parallel with the IOC IIO

path including the test-indicating instrument and the conductor ofunknown resistance and also in parallel with the remaining two sides ofthe quadrilateral conductor together, while the said conductor Z isconnected at one end between the test-indicating instrument and theconductor of unknown resistance, substantially as described. v

8. The combination with a source of current, of terminals a, b, thereof,a terminal c, tho terminals Z9 and e being adapted for connection withthe terminals of the conductor of unknown resistance, a test-indicatinginstrument Zt interposed between the terminals a and c, resistance-wirei, Zt', uniting the terminals a and b, the source of vcurrent beingincluded in parallel with the current-path including the test-indicatinginstrument and the conductor of unknown resistance in series, and alsoin parallel with the wire t', 7c, and a conductor Z attached at one endto the terminal c and provided at the other end. with a stylus m adaptedto make contact with any portion of the wire t', Za, whereby the amountof resistance in shunt of the test-indicating instrument and theconductor of unknown resistance may be adjusted to determine the amountof the unknown resistance in the conductor under test, substantially asdescribed. l

4. The combination with a source of current, of terminals a and bthereof, a terminal c, the terminals Z) and c being adapted forconnection with the terminals of the cond uctor of unknown resistance, atest-indicating telephone-receiver h interposed between the terminals ctand c, resistance-wire t, Zt, uniting the terminals a and l?, the sourceof current being' included in parallel with the current-path includingthe test-indicating telephone and the conductor of unknown resistance inseries, and also in parallel with the wire ft', Zt', and a conductor Zattached at one end to the terminal c and provided at the other end witha stylus fm adapted to make contact with any portion of the wire t', Zo,whereby the amount of resistance in shunt of the test-indicatingtelephone and the conductor of unknown resistance may bevadj usted todetermine the amount of the unknown resistance in the conductor undertest, substantially as described.

5. The combination with a source of current, of terminals ct, Z9,thereof, a terminal c, the terminals b and c being4 adapted forconnection with the terminals of the conductor of unknown resistance, atest-indicating instrument hinterposed between the terminals a and c,resistance-wire t', Zo, uniting the terminals a and b, the source ofcurrent being included in parallel with the current-path including thetest-indicating instrument and the conductor of unknown resistance inseries, and also in parallel with the wire t', 7c, a conductor Zattached at one end to the terminal c and provided at the other end witha stylus lm. adapted to make contact with any portion of the wire fZ,Za, whereby the amount of resistance in shunt of the test-indicatinginstrument and the conductor of unknown resistance may be adjusted todetermine the amount of the unknown resistance in the conductor undertest, and a calibrated scale along tho wire t', 7a, for indicating themeasurement of the resistance of the conductor under test, substantiallyas described.

6. The combination with a source of current, of terminals ct and bthereof, aterminal c, the terminals b and c being adapted for connectionwith the terminals of the conductor of unknown resistance, atest-indicating telephone-receiver h interposed between the terminals ctand c, resistance-wire 1.', Za, uniting the terminals ct and Z), thesource of cur? rent being included in parallel with the current-pathincluding the test-indicating telephone and the conductor of unknownresistance in series, and also in parallel with the wire t', 7c, aconductor Z attached at one end to the terminal c and provided at theother end with a stylus m adapted to make contact with any portion ofthe wire 1l, 7o, whereby the amount of resistance in shunt of thetest-ini IOO

